Coil construction



y 965 n. F. BROWER ETAL 3,1 95;335

COIL CONSTRUCTION Filed D80. 7, 1962 United States Patent 3,195,335 COILCONSTRUCTION David F. Brewer, San Diego, and Gannon B. Hayward,

Del Mar, Califi, assignors to General Dynamics Corporation, New York,N.Y., a corporation of Delaware Filed Dec. 7, 1962, Ser. No. 243,010 7Claims. (Cl. 7256) The present invention relates to a forming deviceand, more particularly, to an improved forming coil assembly for anelectromagnetic forming apparatus.

In recent years, methods and apparatus have been developed for formingmaterial by employing magnetic fields of high flux density. In suchapparatus, a magnetic field of high flux density is set up about ashapedconductor by passing a current pulse of high amperage through theconductor. This high density pulsed, magnetic field induces a current ina conductive work piece disposed in the magnetic field, which current isconcentrated on the surface of the work piece. This induced current isalways in such a direction as to tend to exclude the magnetic field fromthe work piece. This results in pressure being applied to the workpiece, which is equal to the energy density of the magnetic field. Thispressure is' made sufficiently high to form the work piece.

' The shape of the conductor or forming coil assembly employed in suchapparatus depends upon the shape of the work piece and the desired endproduct. Because it is desirable to accomplish diverse formingoperations with a single forming coil assembly, the coil assembly ispreferably designed to accommodate various sizes and shapes of workpieces.

An object of the present invention is the provision of an improvedforming coil assembly for an electromagnetic forming apparatus. Anotherobject of the invention is the provision of a forming coil assembly foran electromagnetic forming apparatus, which assembly can be adapted toform diverse shapes of work pieces. A further object is the provision ofa forming coil assembly for an electromagnetic forming apparatus, whichcoil assembly is efficient in operation and has a relatively highstrength. Still a further object is the provision of an electromagneticforming coil assembly which is relatively inexpensive to manufacture anddurable in use.

Other objects and advantages of the present inventionwill becomeapparent with reference to the following description and accompanyingdrawings.

In the drawings:

FIGURE 1 is a side View of an electromagnetic form ing coil'embodyingvarious features of the present invention, portions of the coil assemblybeing broken away to better illustrate certain parts thereof;

. FIGURE 2 is a plan View taken along line 22 of FIGURE 1, portionsthereof being broken away to better illustrate certain parts thereof;

FIGURE 3 is an enlarged perspective view of a portion of the coilassembly shown in FIGURES 1 and 2; and

FIGURE 4 is a cross sectional view taken generally along line 44 ofFIGURE 1.

In the drawings, a forming coil assembly is shown which is adapted to bemounted in an electromagnetic forming apparatus. Generally, the formingcoil assembly includes an annular core of conductive material and a coil12 of conductive material which is disposed about and insulated from theconductive core 10. A generally cylindrical field shaping element 14 ofconductive material is removably-disposed within the space defined bythe annular core 10. I The field shaping element 14 is provided with anaperture 16 for receiving the work piece to be formed, and a slot 18extending between the outer surface thereof and the aperture 16. Thesurface of the field shaping element 14 facing the annular core 10 ispro- 3,125,335 Patented July 20, 1965 ice vided with means 29 forelectrically insulating the field shaping element 14 from the core 10.

More specifically, the illustrated forming coil assembly is adapted tobe clamped in position on an electromagnetic forming apparatus (notshown). One such electromagnetic forming apparatus is disclosed andclaimed in a pending application, Serial No. 171,333, filed February 6,1962,

now U.S. Patent No. 3,114,585. The apparatus generally includes a sourceof pulsed current and a control circuit therefor. A clamp is alsoincluded in the apparatus which clamp is designed to clamp the hereindisclosed forming coil assembly in position on the forming apparatus.The clamp is also designed to make a ground connection and a highvoltage connection with the forming coil assembly.

In the illustrated embodiment, the forming coil assembly includes thecoil or solenoid 12 which is formed of a tubular conductor 22 composedof a material such as copper, beryllium copper, etc. The end portions 24and 26 of the conductor 22 extend generally radially from the coil 12.

I water through the conductor 22.

3 by a suitable plug 30. The other end 26 of the conductor 22 isprovided with a coaxial coupling 32 which is adapted to connect the tubeto a source of coolant (not shown) which may be included in the formingapparatus. Thus a continuous path for the cooling medium is providedwhich extends from the coupling 32 through the annularpassage providedbetween the tube 28 and the conductor 22 to the plugged end 24 and thenback through the tube 28 to the coupling 32.

The magnetic field established by a pulsatory current passing throughthe coil 12 is concentrated by a flux concentrating means 34, whichincludes the annular core 10 and the removable, generally cylindricalfield shaping element 14 disposed within the space defined by theannular core 10. The annular core 10 is made of a high strengthconductive material, such as beryllium copper, copper, etc., and isdisposed within the coil 12 with the outer surface thereof in contactwith the coil 12. To reduce the repulsion force between the coil 12 andthe core 10 and also to provide a close electrical coupling between thecore and the coil, the coil 12 is disposed within a helical groove 36provided in the exterior surface of the annular core 10. The coil 12 isinsulated from the annular core 10 by a tube 38 of insulating materialdisposed on the conductor 22.

The annular core 10 is provided with a radially extending slot 40 toprovide a path for the current induced in the core to flow between theexternal surface and the internal surface thereof. A piece of insulatingmaterial 42,.

such as fiber glass reinforced plastic, is disposed within the slot 41)to maintain the desired size of the slot. As

shown particularly in FIGURE 1 the coil 12 is struc element 14 isdisposed within the space defined by the annular core 10. Theillustrated field shaping element 14 is generally cylindrical in outlineand is made slightly smaller in diameter, than, the internal diameter ofthe.

annular core 10. The field shaping element 14 is made of a conductivematerial, such as copper, beryllium copper, etc. The element 14 iselectrically insulated from the core. by means 263 which includes awrapping of high.

. shown) to be formed. One end of the element 14 is provided with acircular cavity 52 which is larger in diameter than the aperture 16 sothat the forming of the work piece is accomplished only at the other endportion of the element 14. This other end portion of the element 14 isprovided with additional structural reinforcement by providing the outersurface thereof with a groove 54, which groove is filled with thewrapping 20 of plastic-impregnated fiber glass roving. The slot 18 whichextends from the external surface of the element Bite the internalsurface thereof, is provided in the element 14 to provide a pathfor thecurrentinduced in the external surface to flow to and from the internalsurface thereof. The slot 18 is filled with an insulating material 58,such as plastici-rnpregnated fiber glass, to

prevent the wrapping of fiber glass roving from reducing v shapingelement 14 is retained Within the annular core by a pair of retainingrings 60 and 62. Each. of the rings 60 and 62 .is made of an insulatingmateriahsuch as plastic-impregnated fiber glass, and is suitably securedto the end of the core 10, as by bolts 6 The internal diameter of therings 60 and 62 is made slightly less than the external diameter of theelement 14 so as to thereby retain the element 14 in place and yet notinterfere with the insertion of the work piece in the element 14.

The shape and size of the aperture in the field shaping element 14depends upon the work piece to be formed and the final product desired.For other shapes or sizes of work pieces, other field shaping elementshaving appropriate apertures which may be, for example, square ortriangular in cross section, are substituted fo the described fieldshaping element.

The illustrated forming coil assembly is connected to the groundconnection and is supported within the clamping device of theelectromagnetic forming apparatus by a radially extending generallyfiat, rectangular mounting bracket 66. As shown in FIGURE 2, themounting bracket 66, which is of laminated construction is connected tothe annular core 10 by an integral extension Til of a relatively thickouter or structural layer 68 of the.

bracket 66, which layer 68 is made of structural and conductivematerial, such as brass, etc. The extension '70 is curved to correspondto the core ill and is mounted to.

the core 10 by suitable means, such as bolts 72. The inner surface ofthe extension 70 is provided with a recess for receiving theplastic-impregnated fiber glass roving 44 surrounding the coil 12.

The supply end 26 of the coil 12 is extended through:

an aperture 74 in the extension 70 and the coupling 32 is electricallyand mechanically secured thereto, as by of the structural layer 68. Theend portion 24 is insulated from the structural layer 68 by aninsulating layer '78 of insulating material, such as plastic-impregnatedfiber glass.

The insulating layer F8 is generally rectangular in shape and isslightly larger than the structural layer 63. The inner surface of thestructural layer 68 is provided with a rectangular channel 38 adiacentthe closed end portion 24 which receives a corresponding projection fillon the insuiating layer 73'. An aperture 92is provided in the insulatinglayer 7% parallel to the'projection 9i) for affording passagetherethrough of the end portion 2 The insulating layer 78 is suitablyconnected to the structural layer es, as by bolts 93.

As shown in FTGURES 1 and 4, the face of the insulating layer73 isprovided with a generally rectangular recess 94 for receiving a platecontact member 96 which makes Contact with the high voltageconnection ofthe clamping device. The plate member 96 is formed of two parallel platemembers 93 and Mid which are provided withopposed grooves 1&1 forreceiving the closed end portion 24 of the coil 12. The plate members 9%and ltitl arerclamped tightly about the uninsulated end portion 24 bysuitable means, as by bolts 3:92. The plate member 9 6 is provided withan elongated rectangular projection lfi-iwhich extends parallel to theend portion 24 and is received in a corresponding recess 106 in theinsulating layer 78. The thickness of the plate member 96 is madeslightly greater than the depth of the recess 94 in'the insulating layer73 so that the surface, of the plate member 96 extends beyond thesurface of the insulating layer '78 and makes good contact with the highvoltage connection.

The disclosed forming. coil assembly has a relatively high strength andis relatively efficient in operation. In this connection, there is aclose coupling between the coil and the fiux concentrating means. Inaddition, each of the parts which is under mechanical strain,-isreinforced by a high strength material. Also, the .field shaping elementmay be easily removed and replaced by other elements.

1 Various changes and modifications may be made in the above identifiedforming coil assembly without departing or deviating from the spirit orscope of the present invention.

Various features of the present invention are set forth in theaccompanying claims.

- What is claimed is:

1. In an electromagnetic forming apparatus, a forming coil assemblycomprising a slotted annular core of conductive material, an insulatedcoil of conductive material disposed on said core, a generallycylindrical field shaping 2. In an electromagnetic forming apparatus,aforming coil assembly comprising a slotted annular core of conductivematerial, said core having a helical groove on the outer surfacethereof, an insulated coil of conductive material disposed in saidgroove, a generally cylindrical field shaping element of conductivematerial removably disposed in said core, said element having anaperture therein and a slot extending between the outer surface of saidelement and said aperture, anda wrapping of electrically insulatingmaterial disposed on said field shaping element for electricallyinsulating said field shaping element from said core.

3. In an electromagnetic forming apparatus, a forming coil assemblycomprising a slotted annular coreof conductive material, an insulatedcoil of conductive material disposed on said core, a generallycylindrical field shaping element of conductive materialremovablydisposed in said core, said element having an aperture therein and aslot extending between the outer surface of said element'and saidaperture, a Wrapping of insulating and structural material on said coil,and a second Wrapping of insulating and structural material on saidfield shaping element.

4. In an electromagnetic forming apparatus, a forming coil assemblycomprising a slotted annular core of conductive material, an insulatedfluid cooled coil of conductive material disposed on said core, saidcoil including a tubular conductor closed at one end, a tube ofinsulating material extending through said conductor to a positionadjacent said closed end, and means for coupling said tube and saidconductor to a source and sink of cooling fluid, a generally cylindricalfield shaping element of conductive material removably disposed in saidcore, said element having an aperture therein and a slot extendingbetween the outer surface of said element and said aperture, and awrapping of electrically insulating material disposed on said fieldshaping element for electrically insulating said field shaping elementfrom said core.

5. In an electromagnetic forming apparatus, a forming coil assemblycomprising a slotted annular core of conductive material, said corehaving a helical groove on the outer surface thereof, an insulated coilof conductive material removably disposed in said groove, a generallycylindrical field shaping element of conductive material disposed insaid core, said element having a circular aperture therein and a slotextending between the outer surface of said element and said aperture,said aperture being reduced in diameter adjacent one end of saidelement, an annular groove in the circumferential surface of saidelement opposite said one end of said element, and a wrapping ofinsulating and structural material on said element.

6. In an electromagnetic forming apparatus, a forming coil assemblycomprising a slotted annular core of conductive material having ahelical groove on the outer surface thereof, an insulated tubularconductor wrapped about said core and disposed in said groove to therebyform a coil, a tube of insulating material disposed within saidconductor and extending from one end thereoi to the other, said tubebeing of a diameter such as to form an annular passage between the sameand said tubular conductor, means for closing the one end of saidtubular conductor, means for connecting said closed end and said openend of said coil to a source of power, a wrapping of high strengthnon-conductive material disposed about said coil and said core, agenerally cylindrical removable field shaping element of conductivematerial disposed Within said conductive core, means for retaining saidelement within said core, said element having an axially extendingaperture therein and a slot extending between the outer surface thereofand said aperture, and a wrapping of plastic impregnated fiberglassroving insulating material disposed about said element.

7. In an electromagnetic forming apparatus, a for ing coil assemblycomprising a slotted annular core of conductive material having ahelical groove on the outer surface thereof, an insulated tubularconductor wrapped about said core and disposed in said groove to therebyform a coil, the ends of said conductor extending generally radially incircumferentially spaced relationship from said core, a tube ofinsulating materialextending through said conductor and terminatingadjacent one end of the conductor, said tube being of a diameter such asto form an annular passage between the same and said tubular conductor,means for closing the one end of said tubular conductor, means forconnecting the other end of said conductor and said tube to a source andsink of coolant, means for connecting said other end and said one end ofsaid conductor to a source of power, a wrapping of high strengthnon-conductive material disposed about said coil and said core, agenerally cylindrical field shaping element of conductive materialdisposed within said conductive core, means for retaining said elementwithin said core, said element having an axially extending aperturetherein and a slot extending between the outer surface thereof and saidaperture, said aperture being reduced in diameter adjacent one end ofsaid element, the outer surface of said element being provided with anannular groove opposite said reduced diameter portion of said element,and a wrapping of high strength insulating material disposed about saidelement.

References Cited by the Examiner UNITED STATES PATENTS 3/64 Brewer etal. l5310 OTHER REFERENCES CHARLES W. LANE-1AM, Primary Examiner.

1. IN AN ELECTROMAGNETIC FORMING APPARATUS, A FORMING COIL ASSEMBLYCOMPRISING A SLOTTED ANNULAR CORE OF CONDUCTIVE MATERIAL, AN INSULATEDCOIL OF CONDUCTIVE MATERIAL DISPOSED ON SAID CORE, A GENERALLYCYLINDRICAL FIELD SHAPING ELEMENT OF CONDUCTIVE MATERIAL REMOVABLYDISPOSED IN SAID CORE, SAID ELEMENT HAVING AN APERTURE THEREIN AND ASLOT EXTENDING BETWEEN THE OUTER SURFACE OF SAID ELEMENT AND SAIDAPERTURE, AND A WRAPPING OF ELECTRICALLY INSULATING MATERIAL DISPOSEDBETWEEN SAID FIELD SHAPING ELEMENT AND SAID CORE.